This invention relates generally to energy absorbing devices, and more particularly, to energy absorbing subassemblies for use in mechanical systems for controlled energy absoprtion.
The speed and power of motor vehicles has led to the development of numerous occupant protection systems designed to absorb or divert the energy of collisions. In frontal impact vehicle collisions, the driver is thrown forward due to inertia, striking the head, neck and chest against the steering wheel and inducing massive trauma. Many approaches have been taken to designing collapsible or otherwise energy absorbing steering wheels and column assemblies to reduce this type of injury. Most mechanical designs, apart from the well-developed air bag technology, utilize an inner shaft and an outer supporting post assembly in a telescoped arrangement, with energy absorbing elements mechanically interposed between or otherwise connected to the inner and outer elements. A deficiency of most prior art designs is a force displacement curve with excessive slope and high initial peak load forces in the region of initial movement of the column system.
For example, U.S. Pat. No. 3,457,800 discloses a steering column assembly comprising an upper and lower steering column shaft engaged to each other. A jacket tube rotatably supporting the upper steering column shaft, is supported by a clamp member which allows it to slide in the lower direction. A plastically deformable impact absorbing means, will absorb the impact, while the lower steering column shaft, including the flexible member will not transmit any harmful effect to the steering wheel.
U.S. Pat. No. 3,597,994 discloses a tubular steering column having telescopic portions arranged coaxially arranged about the steering shaft and an energy-absorbing member capable of plastic deformation under tension or compression.
U.S. Pat. No. 3,665,777 discloses a steering column assembly which includes an energy absorbing outer jacket and a telescopically collapsible steering shaft. The shaft has a resilient friction member separating the inner and outer shaft components. The friction member is radially compressed between the two components to maintain the relative position of the shaft components and prevent vibration.
U.S. Pat. No. 5,507,203 discloses a steering shaft coupling which contains an outer tubular shaft and an inner shaft slidably inserted within the outer tubular shaft. Additionally a biasing member positioned between the inner and outer shafts, produces a force which opposes the transmitted torque.
U.S. Pat. No. 6,109,652 discloses a steering column with upper and lower columns and a shock absorbing device therebetween. The shock absorbing device has a plurality of friction members, which contact the external surface of the lower column. The shock absorbing device effectively absorbs and relieves shock in the initial stage of a collision, protecting the driver.
U.S. Pat. No. 6,170,862 discloses a collapsible steering column that has an elongated hollow cylinder slidably mounted on a piston. The space between the interior wall of the cylinder and the piston is sealed in a gas-tight fashion. A coil spring inside the cylinder urges the piston and the bottom of the cylinder apart. When a collision occurs, the sensor sends an electronic signal which ignites the explosive compound and fractures the seal permitting the gas to escape, causing collapse of the cylinder.
U.S. Pat. No. 6,339,970 discloses a steering column which is telescopic in the event of a crash. The outer column tube is connected to a stem by means of a shearing body. The shearing body has a shearing area which is reduced relative to its external dimensions and determined by a projection connecting its two sections. This allows the shearing body to absorb relatively large axial forces and still permit maximum admissible shearing forces.
These prior art designs all have an outer tube that is deformable upon impact to thereby absorb energy. However, the energy absorption is not smooth, but occurs abruptly in early stages as various segments of the outer tube begin to plastically deformed.
U.S. Pat. No. 3,699,824 discloses an energy absorbing steering column having a pair of telescopic steering shaft sections and a pair of telescopic tubular sections that form an outer housing. The tubular sections are separated by a plurality of pre-stressed elastomeric members that are compressed when the column is collapsed thereby absorbing energy.
U.S. Pat. No. 3,757,601 discloses a tube assembly which includes a first tube section and a second tube section telescopically disposed relative to the first tube section. A plurality of spring pins are disposed between the tube sections to generate mechanical friction to effect energy absorption at a predetermined rate during forced telescopic collapse of the tube assembly.
U.S. Pat. No. 5,669,633 discloses two tubular members which are axially displaceable. One of the tubular members contains tear-off strips with bent-over front ends having bent-over sections engaging the other tubular member. Consequently, once a relatively large force is applied to the steering shaft along the flutes, the strips are torn off and deformed, causing displacement of the members relative to each other.
These prior art designs employ a lower column interferentially fitted into the upper column to form a shock absorbing device in the interferential fitting junction between the columns. The shock absorbing device includes anything from a plurality of pre-stressed elastomeric members or tear-off strips, to a plurality of spring pins which are disposed between the tube sections to generate friction. In the event of a collision, the lower column frictionally retracts into the upper column, absorbing energy and relieving the collision impact. However, at peak force, a relative displacement between the two columns can occur, thus, preventing the lower column from gradually retracting into the upper column, and transmitting excessive axial force to the steering wheel.
U.S. Pat. No. 3,392,599 discloses a collapsible steering column assembly which includes a pair of telescopically related cylinders with a plurality of hard spheroids engaged between the cylinders. Thus, once impact energy is applied to the steering column, the spheroids cause highly localized deformation in the contact surfaces of the cylinders.
U.S. Pat. No. 3,538,783 discloses two telescoping tubular members with a sleeve containing press-fitted balls. The sleeve and ball unit is placed to be engaged between the members creating substantial interference so as to roll and cause localized deformation of the members under telescopic movement.
U.S. Pat. No. 5,495,777 discloses a steering column which includes a tubular lower mast jacket, a tubular upper mast jacket telescoped inside the lower mast jacket, and a plurality of steel spheres fitted in an overlap between the mast jackets. A plastic ball sleeve contains pockets which loosely receive the steel spheres and prevent the spheres to roll freely. Thus, a significant amount of force is required to exceed the pockets and cause collateral damage to the steering column.
These prior art designs utilize spherical elements or rigid balls press-fitted in and between two telescopically engaged posts so that under impact the posts exhibit axial relative movement and the rigid balls cause localized plastic deformation of the wall surfaces of the posts along their spherical paths. However, one disadvantage of this design is that a high magnitude of initial load is needed to start the telescopic contraction of the posts. To better control by design this high magnitude of initial load, the shock absorbing characteristics of the apparatus have to be lowered so that furthered loads absorbed by the apparatus will be abruptly decreased. Thus, the impact absorption gradient is not optimal.
Finally, U.S. Pat. No. 4,006,647 utilizes spherical elements press-fitted between two telescopically engaged cylindrical members. The spherical elements are guided to roll within recessed grooves in the outer cylindrical member. The spherical elements make almost no contact with the adjacent wall of the cylindrical member, thus only exhibiting a minor load influence. However, when the relative movement of the two cylindrical elements exceeds the maximum force, the spherical elements reach the ends of the guide grooves and are forced to ride over the surface of the cylindrical member and are pressed between the two cylindrical members causing localized plastic deformation of the surfaces of the walls. For this to function as intended, the spherical elements must be positioned within the grooves. The grooves act merely to guide the spherical elements until enough force is exerted to displace the spherical element past the ends of the grooves onto the surfaces of the cylindrical member. Additional spherical elements may be positioned adjacent to the grooves and with almost no contact with the adjacent wall surfaces of the posts 1 and 2 or very slight contact therewith only having a minor load influence thereon. An inherent disadvantage of this design is that the initiating and continuous collapse forces required to effect energy absorption by the steering column assembly can not be finely tuned according to precise parameters. Thus an initial peak load force is required in order to displace the spherical elements within the guide grooves, and a high peak load force is required to displace the spherical elements past the ends of the grooves and this higher load required to continue collapse of the steering column.
Plot xe2x80x9cpaxe2x80x9d in FIG. 6 represents the displacement force profile of a collapsible steering column of the prior art, wherein the initial displacement force spikes very high, to for example 900 LBF. or greater, and then decreases down to a constant collapse force of around 800 LBF. This represents the undesirable mechanical characteristics of a high force required to initiate collapse (more likely to cause trauma to vehicle occupant), and a decline thereafter to the constant collapse force.
These are some of the major disadvantages of collapsible or energy-absorbing steering columns of the prior art which are overcome by the present invention.
The present invention provides an impact energy absorbing steering column which absorbs impact energy in a multistage non-linear manner by gradually collapsing, without the occurrence of an initial peak load, and thus, is tunable to a precise collapse load range.
In accordance with one general aspect of the present invention, there is provided a tunable non-linear energy-absorbing column assembly having an outer sleeve, an inner tube, a bearing sleeve over the inner tube, wherein the inner tube and bearing sleeve are telescopically received within the outer cylindrical sleeve. The outer sleeve, inner tube and bearing sleeve are also referred to collectively as components of the column assembly. The outer sleeve includes a receiving end which accepts an insert end of the inner tube, and a mounting end. An insert end of the inner tube is telescopically received within the outer sleeve. The bearing sleeve houses one or more spherical elements in contact with the inner tube and the outer sleeve. The bearing sleeve is positioned over the insert end of the inner tube and then both the bearing sleeve and the inner tube are telescopically received within the outer sleeve. Two or more radially spaced serrations are made in the insert end of the inner tube, forming deflection tabs in the inner tube. The spherical elements housed within the bearing sleeve are radially offset from the serrations in the inner tube to bear directly on the deflection tabs. The extent of deflection of the deflection tabs inward toward the axis of the inner tube is a function of the position of the spherical elements along the length of the tabs. An axial force applied to the column assembly causes the inner tube to telescope further inside the receiving end of the outer sleeve, within the bearing sleeve and in contact with the spherical elements. Movement of the spherical elements relative to the length of the deflection tabs gradually increases the amount of force required to continue telescopic collapse of the steering column assembly. Thus, the number, size and spacing of the deflection tabs can be finely tuned to precisely control the amount of forced required to initiate and continue collapse the steering column assembly.
In accordance with another aspect of the present invention, there is provided a steering column assembly which does not contain a separate outer sleeve. The non-linear energy-absorbing steering column assembly includes a bracket with a cylindrical opening or bore for telescopically receiving the insert end of the inner tube and the bearing sleeve. The spherical elements in the bearing sleeve contact the bearing surface of the bore in the bracket, and holds the spherical elements in contact with the deflection tabs of the inner tube. The deflection tabs of the inner tube deflect in response to this contact with the spherical elements. The amount of force required to collapse the steering column assembly is still proportional to the amount and length of the radially spaced serrations of the inner cylindrical sleeve.
These and other aspects and principle advantages of the invention are herein described in particularized detail with reference to the accompanying Figures. Among the benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description made with reference to the accompanying drawings. The drawings constitute a part of this specification and include exemplary embodiments, and illustrate various objects, features, attributes and mechanical advantages of the invention.